tree-wide: convert dlopen_*() callers to DLOPEN_* wrapper macros

Switch the executable-owned call sites from the plain dlopen_<lib>()
helpers to the new DLOPEN_<LIB>() macros, so that each binary that loads
an optional library at runtime now carries its own .note.dlopen note
instead of relying solely on libsystemd-shared. Each call site passes a
priority reflecting whether it hard-depends on the library (required) or
degrades gracefully without it (recommended).

Co-developed-by: Claude Opus 4.8 <noreply@anthropic.com>

src/keyutil/keyutil.c

@@ -233,7 +233,7 @@ static int verb_extract_public(int argc, char *argv[], uintptr_t _data, void *us
                                 return r;
                 }
 
-                r = dlopen_libcrypto(LOG_ERR);
+                r = DLOPEN_LIBCRYPTO(LOG_ERR, SD_ELF_NOTE_DLOPEN_PRIORITY_REQUIRED);
                 if (r < 0)
                         return r;